This invention relates to an object detector apparatus and a method of detecting the presence of an object. In particular, the invention relates to an object detector apparatus for detecting the presence of an object which has repetitive motion, such as a rotating cutting tool.
Objects having a repetitive motion can be detected by a detector device receiving a signal from the object. For instance, the detector device can record the signal as a pattern of data and compares the pattern of data recorded with a previously recorded data pattern. If there is a correlation between the pattern of data recorded and the previously recorded data pattern, then the detector device can determine that an object has been detected. Such a detector device for detecting a rotating cutting tool is described in WO-A-06/027577.
However, with such known detector devices, it is necessary that the motion of the object to be detected repeats at a particular predetermined frequency.
It can be important to be able to detect objects across a range of different frequencies. This is because in some circumstances it might not be possible, or desirable, to cause the object to repeat at one particular predetermined frequency.
Further, even if it is possible to cause the motion of the object to be repeated at the required frequency, the object might normally operate at a different frequency. Accordingly, there will be a delay during the changing of operational frequency of the object so that it can be detected. There will also be a delay in changing the speed of the object back to its normal operating frequency.